The present invention relates to a surface-mounted type antenna to be mounted on circuit boards and the like incorporated in communication devices, and further relates to a communication device including the same.
In communication devices such as portable telephones, there are cases where a chip-shaped surface-mounted type antenna is mounted on the circuit board incorporated therein. There are plenty of varieties in the surface-mounted type antennas. One of them is a plural-resonance surface-mounted type antenna.
This plural-resonance surface-mounted type antenna has a dielectric substrate constituted of dielectric body such as a ceramic or a resin, and has two radiation electrodes disposed on the surface thereof, with a space between the radiation electrodes. The resonance frequencies of the two radiation electrodes are set so as to deviate from each other so that the frequency bands of transmitting and receiving waves of these two radiation electrodes partially overlap each other, as indicated by frequencies f1 and f2 in FIG. 10. By resonating the two radiation electrodes which thus slightly differ in the resonance frequency from each other, plural-resonance conditions in frequency characteristics as indicated by the solid line in FIG. 10 is created, whereby widening of the frequency bands of transmitting and receiving waves of the surface-mounted type antenna is realized.
With a view to miniaturizing the surface-mounted type antenna, however, there is a tendency to increase the permittivity of the dielectric substrate and to narrow the gap between the two radiation electrodes. As a result, the capacity occurring between the two radiation electrodes increases, and the capacitive coupling therebetween strengthens, which results in a mutual interference of the resonances generated between the two radiation electrodes. This raises a problem that one of the two radiation electrodes hardly resonates and that a satisfactory plural-resonance conditions thereby cannot be achieved.
Also, when aiming at thinning the surface-mounted type antenna, the distances between the two radiation electrodes and the ground are reduced, and thereby the capacities (fringing capacities) between the radiation electrodes and the ground increase. When the degree of increase in these fringing capacities are remarkable so that the fringing capacities become significantly larger than the capacity between the two radiation electrodes, the problem of being unable of achieving satisfactory plural-resonance conditions occurs, just as in the case described above.
The present invention has been made in view of solving the above-described problems, and aims to present a surface-mounted type antenna of which the miniaturization and thinning has been realized, and which allows superior plural-resonance conditions to be achieved by adjusting the strength of the capacitive coupling between the two radiation electrodes, and aims further to present a communication device provided therewith.
In order to achieve the above-described objects, the present invention has the following constructions as means for solving the above-described problems. A surface-mounted type antenna in accordance with a first invention comprises a dielectric substrate, a first radiation electrode formed on the dielectric substrate, and a second radiation electrode disposed on the dielectric substrate at a predetermined distance from the first radiation electrode. In this surface-mounted type antenna, there is provided capacitive-coupling adjusting means which makes the permittivity between the first radiation electrode and the second radiation electrode differ from that of the dielectric body, and which varies the strength of the capacitive coupling between the first radiation electrode and the second radiation electrode.
A surface-mounted type antenna in accordance with a second invention has the construction of the first invention, and is characterized in that the capacitive-coupling adjusting means thereof is constituted of a recess or a groove in which a capacity occurs and which is formed between the first radiation electrode and the second radiation electrode, in the surface of the dielectric substrate.
A surface-mounted type antenna in accordance with a third invention has the construction of the first invention, and is characterized in that a permittivity adjusting material portion which has a different permittivity from that of the dielectric substrate is interposed between the first radiation electrode and the second radiation electrode and that this permittivity adjusting material portion constitutes capacitive-coupling adjusting means.
A surface-mounted type antenna in accordance with a fourth invention has the construction of the first invention, and is characterized in that the capacitive-coupling adjusting means is constituted of areas of the first radiation electrode and the second radiation electrode, the area being a hollow portion situated inside the dielectric substrate.
A surface-mounted type antenna in accordance with a fifth invention comprises a dielectric substrate, a first radiation electrode formed on the surface of the dielectric substrate, and a second radiation electrode disposed on the surface of the dielectric substrate at a predetermined distance from the first radiation electrode. This surface-mounted type antenna is characterized in that the dielectric substrate is formed by bonding a first dielectric substrate and a second dielectric substrate which has a different permittivity from that of the first dielectric substrate, that the first radiation electrode is formed on the first dielectric substrate while the second radiation electrode is formed on the second dielectric substrate, and that the bonded portion between the first dielectric substrate and the second dielectric substrate is disposed in the space which is situated between the first radiation electrode and the second radiation electrode and in which a capacity occurs.
A communication device in a sixth invention is characterized in that it is provided with a surface-mounted type antenna which has a construction of any one of the first through fifth inventions.
In the invention having the above-described features, for example, the capacitive-coupling adjusting means makes the permittivity between the first radiation electrode and the second radiation electrode differ from that of the dielectric body. As a result, the strength of the capacitive coupling in the space which is situated between the first radiation electrode and the second radiation electrode and in which a capacity occurs, varies in the xe2x80x9cstrongerxe2x80x9d direction or in the xe2x80x9cweakerxe2x80x9d direction according to the permittivity between the first radiation electrode and the second radiation electrode, than the case where the permittivity between the first radiation electrode and the second radiation electrode is the permittivity of the dielectric substrate. In the present invention, since the strength of the capacitive coupling in the space which is situated between the first radiation electrode and the second radiation electrode and in which a capacity occurs, can be adjusted, it is possible to inhibit the mutual interference of the resonances of the first radiation electrode and the second radiation electrode, and to thereby improve antenna characteristics, while achieving the miniaturization and thinning of the surface-mounted type antenna.